PP1 The Peppered Moth: The Proof of Darwinian Evolution Michael E. N. Majerus Thankyou XX I am delighted to be here at my first ESEB conference. Today I want to talk to you about one of the best known, and, over the last decade, most controversial examples of Evolution in Action, that of industrial melanism in the Peppered moth, Biston betularia . The case reached a prominence as one of the most cited examples of Darwinian evolution in action because of the visual impact of the case, the ease with which it can be understood by non-specialists, and because empirical evidence was collected, in the 1950s, to show the selective agent responsible for the changes that had been observed. I am sure that most of you know the peppered moth story, but just as a resume, in brief the story was this: PP2 The non-melanic, or typica peppered moth is white, liberally speckled with black. (Typica ) PP3 In 1848, a black form, f. carbonaria was recorded in Manchester. (Fact + carbonaria) PP4 By 1895, 98% of the Mancunian peppered moths were black. The carbonaria form spread to many other parts of the UK, reaching high frequencies in industrial centre and regions downwind. In 1896, the great Victorian lepidopterist, J.W. Tutt hypothesized that the increase in carbonaria was the result of differential bird predation favouring carbonaria in polluted regions, but not in unpolluted regions. Nothing much happened for the next half century, except that Haldane showed that carbonaria would have to have been one and a half times as fit as the typical form, to explain its observed increase in frequency in Manchester. In the 1950s, Bernard Kettlewell obtained data from direct predation experiments, and mark-release- recapture experiments, in two woodlands, one polluted, the other relatively unpolluted, that supported Tutt’s hypothesis. PP5 It was the reciprocal nature of Kettlewell’s results in the two woodlands, allied to extensive survey work showing a strong correlation between carbonaria frequency and industrial pollutants that made the case so persuasive. Over the next 40 years, various researchers worked with peppered moths to tease apart the fine detail of the case, but none of the new findings seriously undermined Tutt’s hypothesis or Kettlewell’s evidence in support of it. Need NEW YORK TIMES PP6 The zenith for the case came in 1996, when, reporting work from both sides of the Atlantic that showed similar changes in melanic frequencies were correlated to pollution levels (Grant et al., 1996), The New York Times featured the peppered moth on the front page of its science section. However, since Kettlewell’s experiments, the black peppered moth has suffered two types of decline. First, following anti-pollution legislation in the 1950s and thereafter, carbonaria began to decrease in frequency, as would be expected from Tutt’s theory. Second, the reputation of the case as an example of Darwinian evolution in action has been severely tarnished. PP7 Today, I want to briefly explain the reason for the case’s decline in reputation. I will then detail why I chose to undertake a piece of experimental work that has taken me 7 years, before presenting you with a series of observations on the natural resting sites of the peppered moth, and the results of two field experiments. Finally, at the end, I may make a few mild concluding remarks. PP8 The decline in the peppered moth’s reputation may be sourced to a book that I wrote in 1998 (show book) , or, more correctly PP9 a review of it by Jerry Coyne, in Nature , in which Coyne concluded ‘…. For the time being we must discard Biston as a well-understood example of natural selection in action…’. I, and others, have dealt with this review previously, showing that the review had little to do with what was said in the book. As Donald Frack put it “There is essentially no resemblance between Majerus’ book and Coyne’s review of it. If I hadn’t known differently, I would have thought that the review was of some other book.” PP10 But the damage had been done. Coyne’s review, and an article, titled “Scientists pick holes in Darwin moth theory” by Robert Matthews in the Sunday Telegraph (March, 1999), began to appear on creationist and anti-evolution web-sites. PP11 The creationists began to smell blood, and a series of articles appeared with titles such as: (Second thoughts about the peppered moth , Darwinism in a flutter, The moth that failed , Staple of evolutionary thinking may not be a textbook case, Moth-eaten statistics , The Piltdown moth, Goodbye, peppered moths; a classic evolutionary story comes unstuck ). I should point out that it was about this time, the year 2000, that I first began to formulate the design of the predation experiment that I will tell you about later. But before we come to that, I must mention one other publication that raised the ante. PP12 In 2002, Judith Hooper, an American journalist and writer, published a book called Of Moths and Men: Intrigue, Tragedy and the Peppered Moth , which is, according to the front cover, a riotous story of ambition and deceit. This appalling book is essentially an attack on the peppered moth case, those who have worked on the evolution of industrial melanism, lepidopterists in general, and Kettlewell and Professor E.B. Ford in particular. Need Hooper Book PP13 To cite the front fly-sheet, “ Of Moths and Men is … a fascinating psychological dissection of the ambitious scientists who will ignore the truth for the sake of fame and recognition”. PP14 I do not want to dwell on Hooper’s book for long. Various reputable scientists, from both sides of the Atlantic: Bruce Grant, Bryan Clark, Lawrence Cook, James Mallett, Paul Brakefield, David Rudge, myself, and even Jerry Coyne, who I think might have been feeling a bit guilty about his review of my book, have discussed the many flaws in Hooper’s book. Coyne, for example, in a review in Nature criticizes her ‘flimsy conspiracy theory’ , her theme of ‘ambitious scientists who will ignore the truth for the sake of fame and recognition’ , by which ‘she unfairly smears a brilliant naturalist’ PP15 Coyne concludes: “‘ This issue matters, at least in the United States, because creationists have promoted the problems with Biston as a refutation of evolution itself. Even my own brief critique of the story has become grist for the creationists’ mill. By peddling innuendo and failing to distinguish clearly the undeniable fact of selection from the contested agent of selection, Hooper has done the scientific community a disservice .’ Refer to Hooper Book PP16 So I will give just a single example of the standard of Hooper’s book. If you go to the first page of Chapter 1, the first sentence is, “ To begin at the beginning, the Lepidoptera are divided into two orders: the butterflies (Rhopalocera) and the moths (Heterocera) . Sadly, the scientific accuracy of the book rarely rises from this inauspicious start. PP17 I leave it to David Rudge to comment of the veracity or otherwise of what Bruce Grant calls Hooper’s “relentless suspicion of fraud” aimed at Kettlewell. Rudge (2005) who examines Hooper’s evidence that Kettlewell committed scientific fraud concludes “that Hooper does not provide one shred of evidence to support this serious allegation”. PP18 In 2000, while the peppered moth was under initial attack from anti-evolution lobbyists, I conceived two parts of the work that I am going to describe to: 1 Fill up a major gap in our knowledge of the natural history of the peppered moth: that is, where peppered moths rest in the day, and 2 Check whether various valid criticisms of Kettlewell’s experimental protocols could have altered the qualitative validity of his conclusions, by conducting a new field predation experiment. Hooper’s book caused me to include an additional experiment, involving peppered moths and bats. PP19 The question that I wished to answer with the main predation experiment was: Is differential bird predation sufficient to explain any changes in the frequencies of the typica and carbonaria forms observed over a period of years. Given previous observations in the Cambridge area and other parts of Britain, I knew that the frequency of carbonaria had been declining, and I had no reason to suppose that the decline would not continue. N.B. It was not possible to replicate Kettlewell’s reciprocal design because in no part of Britain is carbonaria frequency increasing. PP20 The main experiment, was designed to take account of all the flaws that had been aimed at Kettlewell’s work, that: i) The densities of moths were too great, and he used too few release sites ii) Moths were released onto tree trunks, when Kettlewell knew that peppered moths usually rest under lateral branches iii) Moths were released during the day, and so might not have selected sites that would maximize their crypsis iv) Kettlewell used mixtures of wild caught and lab bred moths, which might behave differently v) Kettlewell used translocated moths that might have had different behaviours as a result of local adaptation. PP21 My experimental design, which was piloted in 2001, and has already been published (Majerus, 2005) allowed me to: i) Do the experiments in the wild, at low frequency (<10 per hectare per night), and collect back any moths left at each predation run. ii) Release moths in their natural resting positions (initially 103 release sites in a 1 hectare experimental site) iii) Release moths at dusk, into restricted arenas at their natural resting sites, so that they could take up resting positions at the end of their night flight.